A photodiode detector array for an optical encoder includes a sequence of photodiodes having a pitch between adjacent photodiodes that alternates between a first pitch and a second pitch, the second pitch being different than the first pitch. The preferred compositions comprise agriculturally derived materials and are preferably essentially composed of agriculturally derived materials. The forward ends or the rearward ends of the arms, or both, may be at least partly covered by jackets. The supporting member includes a light emitting surface at a side thereof distant from the light emitting diodes.